One of the problems with flow through water valves that are connected to pressurized water sources is that upstream pressure supply conditions can occur that may force water to flow backwards into the water supply. For example if the water supply pressure suddenly drops the water in the pipes may flow backward into the water source. In order to prevent the backflow of water it is necessary to "break the vacuum" or permit air to enter the pipes so the water in the downstream lines can drain out of the system without being forced backward through the water valve and into the water supply. Typically, such prior art devices have relied on a check valve in the down stream water lines to close off and prevent water from flowing backwards into the water source. The present invention provides an improvement over such inventions by providing a valve that does not include a check valve to stop flow but includes a venting region to quickly decrease the pressure in the line to allow the water to be diverted and quickly vented into the atmosphere in response to the lowering of the water pressure in the supply system. The valve is responsive to the lowering of the fluid pressure in the inlet so that reverse flow conditions do not have to occur before the valve begins to begin the process of diverting the fluid through the vents.